1. Field of the Invention
The present invention relates to a heat radiating structure for solid-state image sensors to be used for image pickup devices such as television cameras and video cameras including solid-state image sensors, as well as to a solid-state image pickup device having such a heat radiating structure.
2. Description of Related Art
In recent years, there have been developed, and now in widespread use, 3CCD color cameras (hereinafter, referred to as 3CCD cameras) as an image pickup device using three solid-state image sensors. The structure of such a conventional 3CCD camera is explained below with reference to the accompanying drawings.
FIG. 1 is a schematic sectional view of an image pickup block 10 in a conventional 3CCD camera. As shown in FIG. 1, the image pickup block 10 includes a color separation prism for separating incident light, which has come up through an unshown image pickup lens of the 3CCD camera, into color components, a plurality of solid-state image sensors, and image sensor boards on which the solid-state image sensors are mounted, respectively.
As shown in FIG. 1, the color separation prism is made up of three prism members 1r, 1g, 1b, which are joined together in close contact with one another. The color separation prism constructed like this is a three color separation prism 1 for separating incident light into three color components. Junction interfaces among the prism members 1r, 1g, 1b serve as dichroic mirrors 4, 5. On light-outgoing surfaces of the three prism members 1r, 1g, 1b, solid-state image sensors 2r, 2g, 2b are fixed individually with adhesive.
Referring to FIG. 1, a light beam 7 incident on the three color separation prism 1 is separated by the dichroic mirrors 4, 5 into three color components, i.e. light beams 6a, 6b, 6c of three primary colors of light, and the resultant light beams are received by their corresponding solid-state image sensors 2r, 2g, 2b, respectively. Out of the light beams separated into the three primary colors and reflected by the dichroic mirrors 4, 5, the light beams 6a, 6b are totally reflected again within the prism members 1g, 1b, respectively, thereby being received by the solid-state image sensors 2g, 2b as light beams that form not mirror images (reflected images) but non-mirror images. Image pickup signal processing for the individual light beams received by the solid-state image sensors 2g, 2b, 2r, respectively, is performed by the image sensor boards 3r, 3g, 3b, respectively, so that a color television signal into which the image pickup signals have been synthesized is obtained.
For the conventional 3CCD camera having such a structure described above, there is a need for achieving high-accuracy superimposition of three-color subject images. Poor accuracy of superimposition, i.e. poor accuracy of registration, would lead to occurrence of color differences or moire false signals, resulting in a subtly deteriorated image. Accordingly, in order to prevent any deterioration of registration accuracy, there is a need for reducing external-force loads applied to the respective solid-state image sensors 2r, 2g, 2b. 
Further, a solid-state image sensor, if used under a high-temperature environment, would undergo occurrence of image quality deterioration due to white scratches, life reduction and so on, and therefore needs to be used at a specified temperature or lower. Particularly in recent years, in image pickup devices typified by 3CCD cameras on which solid-state image sensors are mounted, there is a tendency that the ambient temperature of the solid-state image sensors (i.e., internal temperature within the device casing) increases more and more with increasing power consumption that can be attributed to light, thin, short and small dimensions and more multiple and higher functions of the device, making it indispensable to provide a means for cooling the solid-state image sensors.
Therefore, in conventional image pickup devices, there have been proposed various heat radiating structures for efficiently cooling solid-state image sensors while reducing external-force loads applied to the solid-state image sensors (see, e.g., Document 1: Japanese patent application publication No. H1-295575, Document 2: Japanese patent application publication No. 2002-247594, and Document 3: Japanese patent application publication No. 2001-308569).
First, Document 1 proposes a heat radiating structure in which a thermoelectric cooling device mounted on a heat transfer member by screws is placed so as to be in contact with the back face of each solid-state image sensor. Document 1 says that, in such a heat radiating structure, since deformations due to thermal expansion and thermal contraction of each member can be absorbed by backlashes of the screws, forces due to the thermal deformations can be prevented from being applied from the cooling device to the solid-state image sensors.
Also, Document 2 proposes a heat radiating structure in which a thermoelectric cooling device fixed to a heat conducting plate is so placed as to be in close contact with the back faces of the solid-state image sensors with proper force by utilizing the elasticity of the heat conducting plate. Document 2 says that, in such a heat radiating structure, since the cooling device can be put into close contact with the back faces of the solid-state image sensors by utilizing the elasticity of the heat conducting plate, there can be realized an efficient heat radiation.
Document 3 proposes a heat radiating structure using no thermoelectric cooling device in which one end of a metallic component is inserted between the back face of a solid-state image sensor and the image sensor board while the other end of the metallic component is fixed to a metal frame so that heat transferred from the solid-state image sensor to the metallic component is released to the metal frame.